Signal-responsive circuit



May 5, 1959 D. T. WEBB 2,885,630

SIGNAL-RESPONSIVE CIRCUIT Filed Nov. 16, 1955 Mf/i/Vf 7'0 EE ENERG/ZED INVENTOR. OER/L 7.' A/EBB United States Patent O SIGNAL-RESPONSIVE CIRCUIT Deril T. Webb, Norristown, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application November 16, 1955, Serial No. 547,169

3 Claims. (Cl. 323-75) This invention relates to signal responsive circuits or devices, and more particularly to circuits or devices which are responsive to changes in an input signal to produce corresponding changes in an output signal.

There are numerous instances in which it may be desirable, in response to relatively small changes in an input signal, to produce substantially larger changes in an output signal. For example, it is frequently desired, in response to a small change in magnitude of an input signal voltage or current, to produce a relatively large change in current to actuate a relay.

While numerous arrangements have been proposed for this purpose, in general they have suiered from various defects including insufficient sensitivity, complexity, and instability under variations in circuit parameters and power supply.

Accordingly, it is an object of this invention to provide an improved circuit which is responsive to variations in an input signal to produce substantially larger variations in an output signal, and which is simple, inexpensive, stable and highly effective.

Another object of the invention is to provide an improved circuit for actuating a relay in response to relatively small variations in an actuating signal.

A further object of the invention is to provide an improved relay-actuating circuit of the bridge type.

Other objects and features of the invention will be apparent from the description to follow.

In accordance with this invention, a circuit is provided comprising two electron tubes (or sections of a single tube) connected to a source of operating voltage, one tube serving as a control tube and having a control electrode to current of said tube, means eifective upon change of anode current of said control tube to change the anode current of the second tube, and means to be controlled connected to be subjected to an output variation upon change of the anode current of the first tube and to be subjected to a further output variation upon change of anode current of the second tube. In the preferred form of the circuit, the elements form a bridge which is normally balanced but becomes unbalanced in response to variation in an applied signal.

Reference is now made to the accompanying drawing wherein;

Fig. l is a diagrammatic illustration of a preferred embodiment of the invention;

Fig. 2 shows the circuit more clearly in bridge form; and

Fig, 3 shows the equivalent circuit of the bridge.

Referring first to Fig. l, there is shown a first electron tube T1 having a control grid to be connected to a source of negative signal as indicated, this tube preferably being a triode. The cathode of tube T1 is grounded, while the anode is connected through a resistor R1 to a source B+ of operating voltage. A second tube T2 has its cathode connected through a resistor R2 to ground, and has its anode connected directly to the source B+. A

2,885,630 Patented May s, 1959 ICC means to be energized, designated by the rectangle M, is connected between the anode of tube T1 andthe cathode of tube T2. Such means is representative of any device to be energized in response to variation in an input signal. For example, where it is desired to effect operation of a relay in response to variation in the input signal, the means M may be the relay coil.

Tube T2 is also preferably a triode, and its control grid is connected to the junction between resistors R2 and R4 which are serially connected between the source B+ and ground. These two resistors constitute a voltage divider, by means of which a biasing voltage is applied to the grid of tube T2. Resistor R4 is variable in order that the grid bias may be adjusted to give a relatively low current or zero current through the energizable means M in the absence of eective variation of an input signal.

Fig. 2 illustrates more clearly the bridge form of the circuit. It will be seen that the circuit components and connections form a bridge having four arms and four junction points, the junction points being designated for convenience by reference numerals 1 to 4. The first eletron tube T1 has its cathode and anode connected respectively to the rst and second junction points 1 and 2, so that Ithe tube is included in one arm of the bridge. The second electron tube T2 has its cathode and anode connected respectively to the third and fourth junction points 3 and 4, so that this tube is included in a second arm of the bridge opposite the first-mentioned arm. Resistor R2 is connected between the first and third junction points 1 and 3 so as to be included in a third arm of the bridge, while resistor R1 is connected between the second and fourth junction points 2 and 4 so as to be included in the fourth arm of the bridge. The source B+ establishes the junction point 4 at a positive potential relative to the first junction point 1 which is at ground potential. The energizable means M is connected between the second and third junction points 2 and 3.

Considering the operation of the circuit, in the absence of an input signal plate current ows in both of the tubes, but little or no current ows through the energizable means M, due to the fact that the bridge is substantially balanced and there is little or no voltage between points 2 and 3. When a negative signal is applied to the grid of tube T1 the anode current of that tube is decreased, and consequently, there is less voltage drop across resistor R1 and the anode voltage rises. This causes current flow, or increased current flow, through the energizable means M and through resistor R2, with the result that increased positive bias is applied to the cathode of tube T2, thus decreasing the anode current of that tube. Consequently, the current through the energizable means M is further increased. Thus in operation of the circuit, the energizable means M receives increased current in response to decrease of anode current of the iirst tube T1, and receives further increased current in response to decrease of the anode current of the second tube T2. The end result, therefore, is the production of a relatively large output current.

In the preferred form of the circuit as illustrated. in which the cathode of tube T1 is grounded, the applied negative signal drives the tube T1 to cutoff, thus effecting maximum rise of the anode voltage. The consequent increased current flow through resistor R2 produces an increased bias which tends to cut off tube T2. If desired, the selection of values of the circuit components may be ysuch as to cause cutoff of tube T2 in response to the increased current ow through resistor R2, in which case the further increased current through the energizable means M will be a maximum.

Fig. 3 shows the equivalent circuit of the bridge. As shown in this figure the plate resistances RP1 and RPg of tubes T1 and T2 actually constitute resistance arms of the bridge. The effect of an input signal is rst to increase RF1 to cause current flow through M, and second to increase RP2 to cause greater current flow through M.

It will be seen from the foregoing description, that this invention provides a novel circuit which is capable of producing a large output signal variation in response to a small input signal variation.

Another advantage of this circuit is that in its balanced condition it is unaffected by changes of the operating voltage B+; that is to say, such changes will not cause false operation of the circuit. Thus, if the voltage B+ rises, the voltage at each of points 2 and 3 will rise, and the increased positive bias on the cathode of tube T2 will be counteracted by the increase of positive bias on the grid of that tube. Conversely, if the voltage B+ drops, the voltage at each of points 2 and 3 will drop, and the decreased positive bias` on `the cathode of tube T2 will be counteracted by the decrease of positive bias on the grid of that tube. Therefore, a change ofthe voltage B+ will not produce any significant diterence of voltage between points 2 and 3.

A further advantage of the circuit is that where the input signal contains an A.C. ripple component, as where the D.C. signal is derived by rectification of an A.C. signal, the circuit is substantially unaffected by such A.C. component, and therefore, there is little chance of appreciable A.C. hum reaching the energizable means M to cause buzz or chatter of a device such as the relay. Since the control tube T1 is operated at zero cathode bias, positive swings of any A.C. component tend to be limited or clipped by grid conduction, and as the D.C. component quickly drives the grid below cut-01T, negative swings of the A.C. component are ineffective. With the grid maintained below cut-oli, of course there is no output.

By way of example only, in one physical embodiment of the invention, a twin triode tube (type 12AV7) is used to provide the two triodes T1 and T2, with a source B+ of 175 volts. Resistors R1 and R2 have values of 12,00() and 10,000 ohms, respectively. The energizable means M is a D.C. relay whose operating coil has a resistance of 1,500 ohms. The voltage divider R3R4 provides a normal voltage of about 50 volts at the grid of triode T2.

Since, as indicated by the above example, it is possible to use a twin triode tube instead of two separate triodes, the term electron tube employed in the appended claims is intended to designate either an individual tube or a tube section.

assenso While a single preferred embodiment of the invention has been illustrated and described, it will be understood that the invention is not limited to such embodiment, it being contemplated that modifications and further embodiments may be resorted to without departure from the spirit and scope of the invention.

i claim:

l. 1n a system for effecting controlled energization of a device in response to a control signal, a source of unidirectional electrical energy, a device to be energized from seid source, a rst electron tube having at least triode elements. a rst fixed resistor, means serially connecting said tube and said resistor across said source with said resistor connected between the anode of said tube and the positive terminal of said source, a second electron tube, a second iixed resistor, means serially connecting said second tube and said second resistor across said source with the anode of said second tube connected directly to the positive terminal of said source and with said second resistor connected between the cathode of said second tube and the other terminal of said source, means connecting said device between the junction point of said iirst tube and said rst resistor and the junction point of said second tube and said second resistor, said tubes and said resistors being elements of a Wheatstone bridge which normally is substantially balanced so that there is substantially no current iiow through said device, and means for supplying a negative signal to the control grid of said rrst tube, whereby the current conduction in said first tube decreases and this in turn causes decrease of `the current conduction in said second tube, with the result that substantial current is caused to flow through said device.

2. In a system according to claim 1, said second tube having a control grid, and adjustable rneans for supplying a biasing potential to the control grid of said second tube, thereby to enable balancing adjustment of the circuit.

3. A system according to claim 2, wherein the means for supplying a biasing potential to the control grid of said second tube comprises a xed resistor and an adjustable resistor serially connected across said source, and rneans connecting the control grid of said second tube to the junction point of said series-connected resistors.

References Qited in the file of this patent UNTTED STATES PATENTS 1,822,996 Mirick Sept. 15, 1931 2,329,073 Mitchell et al. Sept. 7, 1943 2,369,066 Maxwell Feb. 6, 1945 2,458,644 Ringer et al. Jan. 11, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent No. 2885,30 May 5U 1959 Deril T. Webb It is hereby certified that error appears in the-printed specifica-tion of 'the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 17x7 after "trede to" insert which an input signal may be supplied to change the anode --9 Signed and sealed this 10th day of January IQL SEA L) Attest:

KARL I-L, AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F 'CORRECTION Pai-,ent No. 2,885,630 May 5 i959 Deril Webb It is hereb'r certified that error appears in theprinted specification of the above l'rmmnered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 47V after "trode to" insert which an input signal may be supplied to change the anode --s Signed and sealed this 10th day of January 1961.

(SEAL) Attest:

KARL H., AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

